The major cause of vascular prosthesis failure is occlusion with thrombus related in part to the inherent thrombogenicity of artificial surfaces. Creation of an endothelial lining on the luminal surface of a vascular prosthesis would be beneficial towards the maintenance of long term patency of the graft. The major objective of the proposed research is to understand the interaction of human adult endothelial cells (EC) with substrate-treated vascular prosthetic surfaces as an initial step in understanding mechanisms of vascular graft endothelialization. These interactions will be evaluated with respect to the ability to maintain: - an adherent and morphologically confluent monolayer - a nonthrombogenic surface when EC are attached to prosthetic graft material and subjected to a physiological shear stress using human blood. The major aim of this research is to examine the following variables 1. EC origin (human capillaries vs. human large vessel EC) 2. EC isolation method (collagenase vs. mechanical scraping) 3. EC subcultivation (both method and number of subcultivations) 4. Vascular graft meterial (dacron vs. expanded PTFE) 5. Vascular graft substrate material (gelatin, collagen I/III, Collagen IV, blood, plasma and fibronectin) upon EC-prosthetic graft interactions as they relate to vascular graft endothelialization.